The Section studies the interaction of complex polysaccharide antigens with monoclonal antibodies. In this way the immunodeterminants can be defined, and putative glycoconjugate vaccines can subsequently be prepared. Binding studies on Vibrio cholerae O:1-related oligosaccharides and five monoclonal antibodies have shown that the immunodeterminant for serotype Ogawa is the sole terminal sugar residue of the O-PS. Two IgGs and an IgA showed identical fine specifity, and very similar affinities for the immunodeterminant. The determinant for serotype Inaba is less well defined, and seems to involve the core region of the LPS. Amino acid sequences determined by cDNA cloning indicate that the heavy chain of the antibody plays the major role in defining specificity. A series of conjugate protein-saccharides were prepared by various methods. There is good promise that well defined conjugate vaccines can be made bearing short, simple oligosaccharides. We have developed a rapid and simple method to recover monoclonal antibody from its complex with ligands that show affinities of 10/3 to 10/6 LM-1. The method is superior to dialysis, and far less wasteful. We have developed a new, simple method for the direct preparation of 1,2 cis-glycosides.